The hard disk drive is the principal device used for long term, bulk memory storage in today's computers. The hard disk drive includes a rotating disk and a head gimbal assembly that is attached to actuator arm in the disk drive and that is held thereby closely adjacent to the rotating disk. The head gimbal assembly consists of several distinct components including a suspension, a gimbal, a flex circuit, and a slider with its integral read/write head. The rotating disk is coated with a magnetic or read/write media that is selectively magnetized by a read/write head to store information thereon. In operation, an electric current is provided to the read/write head, which creates and applies a magnetic field to the disk as the disk rotates relative to the head. The current is selectively controlled such that the applied magnetic field selectively reverses, thereby preferentially magnetizing elective areas of the disk. Each magnetized area consists of a north and south pole selectively oriented in one of two preferred directions. Magnetized areas having a north pole pointing in one of the two direction are designated as a “0” and in the other direction as a “1.” In this way the binary language of computers consisting of zeroes and ones is assembled and data and programs, which comprise zeroes and ones in binary computer language, are stored on the hard disk. To read the information, current read/write heads sense changes in the current flowing through the head as the magnetized areas of the disk pass by and recognizes the current changes as a 0 or 1.
Typical hard disk drives include multiple disks and multiple read/write heads. As the disks rotate in the disk drive, air flow from the spinning disks interacts with the bearing surface on the slider to create an air bearing, which is used to place the read/write head at the designed distance from the disk media, also known as the hard disk drive's magnetic spacing. If the head is too far away from the media, signal loss will occur and if the head is too close to the media, the head could mechanically crash, that is, actually come into contact with the disk, resulting in damage to the head or the media and often a complete hard drive failure.
Currently, the hard disk drive industry is striving to increase the amount of data or information that can be stored in a predetermined area. That is, the industry is trying to increase the quantity of information stored per unit area of the disk. To do this, the magnetized disk media areas, which are representative of the stored data, must be smaller and closer together. In turn, this requires that the sliders as well as the magnetic spacing be smaller. As the sliders are made smaller, they become increasingly sensitive to factors causing spacing variation. The key mechanical factors that determine the proper magnetic spacing are the bearing manufacturing tolerances, the load placed on the slider from the suspension, and the torque acting on the slider from the suspension and assembly tolerances.
The performance of the read/write head is critical to the long-term operation of a hard drive. These devices include small component parts operating under extreme conditions. Precision manufacturing and quality control testing of these parts prior to their incorporation into the finished hard disk drive is therefore desirable to ensure that only quality components make it into the disk drives before being sold to the consumer.
One of the critical components in the hard disk drive is the head gimbal assembly. The head gimbal assembly has traditionally been assembled together by hand in several steps. Presently, a head gimbal assembly process includes, broadly stated, steps including the adhesive attachment of a slider to a suspension, the routing of leads to electrically connect the head to the disk drive electronics, and the testing the electrical performance of the head while the suspension holds it over a test disk. Many problems are encountered with the present process resulting in high costs and poor magnetic spacing tolerances.
One of the problems is that the present system is labor intensive. This creates many potential opportunities for the generation of electrostatic charges, which can damage the components with an electrostatic discharge (ESD) or electrical overstress (EOS).
Another example of a problem relates to the electrical connection made between the head termination pads on the slider and the electrical interconnect or flex circuit running along the suspension after the slider is attached to the suspension. These electrical connections are difficult to make for several reasons. For example, the slider is positioned with respect to the gimbal load point and not necessarily the electrical leads on the suspension, which can cause the electrical connection to be difficult and unreliable. In addition, because the intricate surface features of the head/slider and suspension make it difficult to hold in a fixture, the bonding process, which requires a significant force to achieve a good bond, often leads to damage of the suspension.
After attachment of the slider to the suspension, each head is tested while the suspension holds the slider over a rotating testing disk. This test is known as a dynamic electrical test (DET). Current DET test procedures require that the head gimbal assembly be held in the loaded position at the correct magnetic spacing or Z-height with respect to the spinning testing disk, making both loading the assembly and automating this test difficult. In addition, mechanical and head tolerances can cause a poor signal, making it difficult to discern the source of any poor performance. Further, the DET results indicate that a head is bad and must be discarded, then the manufacturer must throw away not only the head/slider but also the suspension to which it is bonded. This is a source for significant yield cost.
Static angles are currently measured with the suspension clamped and held in its loaded state, by lifting the beam with a pin near its center. While the slider bond pad is the point of interest, it is impossible to load it and measure it at the same time, without affecting the static angle. The act of bringing the suspension to its loaded position causes clamping and fixturing to be difficult as well as forces one to account for a pitch bias, because the loading is not at the suspension bond pad. In addition, if the loading mechanism is not perfectly centered on the load beam, the act of loading can cause a roll bias in the angle measurement.
In the past, some have measured static angles in the unloaded condition, but the measurement reference was the plane of the suspension beam and not the mounting plate plane (actuator arm interface). This reference problem resulted in an unpredictable bias between the measured static angles and the real static angles.
Placing the read/write slider on the suspension is primarily a manually process wherein pins or cavities in tooling hold each component in alignment. While the position target is to align the suspension load point to the designed location on the slider air bearing, tolerances make this a difficult task. U.S. Pat. No. 4,866,836 addresses these tolerances by optically aligning the slider body to the suspension (dimple) load point. This technique alleviates the load point source of torque variation, but it does not address the torque from suspension, circuit, bond line parallelism and slider parallelism tolerances.
Several techniques have been attempted to “bond out” the static angles from the suspension and slider (parallelism). These are described in U.S. Pat. Nos. 5,608,590; 5,473,488; 5,661,619; 5,729,889 and 5,636,089. These concepts attempt to counter torque from static angle tolerances by allowing the adhesive to form a wedge between the slider and suspension bonding surfaces. These techniques do not address torque from load point tolerances and the adhesive wedge is difficult to control, at best, thus it does not “bond out” the static angle tolerances.
U.S. Pat. Nos. 5,198,945 and 5,282,102 teach integrated flexure suspensions that reduce some load position errors, but do not address torque from static angle tolerance, bond line parallelism or slider parallelism.
U.S. Pat. No. 5,682,780 is an example of a suspension adjustment technology used to decrease some of the static angle variation from the suspension components, which involves deforming the mechanical suspension. It does not address load point, bond line parallelism or slider parallelism sources of torque.
A technique has been used to measure the torque acting on the slider body and shift the slider relative to the suspension to minimize the torque during slider bonding. This technique is shown in U.S. Pat. No. 5,371,939. While this technique adjusts slider position to account for torque from static angles, load point, and slider parallelism, it requires aligning the slider with the suspension in a loaded position and requires that small actuated fixtures come in contact with the slider body. Bringing the suspension to the loaded position involves precise clamping and very controlled distances between that clamp surface and the loading surface. Thus, inherently, this technique is difficult to automate and achieve high throughput.
The foregoing discussion of current head gimbal assembly procedures has highlighted several of the problems with the current assembly procedures and pointed out the long-felt but unsatisfied needs of the industry. Thus, there is a need for a method of only aligning the head termination pads to the interconnect leads rather than the gimbal load point as well as a need for simplifying the fixturing to reduce damage to the suspension. Also, there is a need for a fast, automatable method for performing a dynamic electrical head test before the head is mounted to a suspension. Yet again, there is a need for a fast, automatable method of mounting a slider without the use of complicated tools and applying a load, which does not damage the suspension and accounts for static angle torques. Additionally, there is a need for a fast, automatable static angle measurement system that does not require loading the suspension, but uses a predictable and functional reference surface. Finally, there is a need for a fast, automatable method to align and attach a slider to a suspension, while accounting for all sources of torque variation.